Therapeutic treatment with some proteins, and particularly immunoglobulins, requires administration of a large dose. Due to their unique ability to recognize and bind to specific targets, immunoglobulins in particular hold great promise for therapeutic treatments in the fights against diseases such as cancer and arthritis. Some drawbacks to treatment with immunoglobulins, however, include low potency on a mass basis due to a typically large molecular weight, a relatively low solubility in water and requirements for effective long-term storage. For example, typical monoclonal IgG antibodies have molecular weights of approximately 150 kDa, have an aqueous solubility limit of less than 50 mg/mL and must be lyophilized for long-term storage.
Also, due to the noted low potency on a mass basis, commercially available therapeutic antibodies have dosing regiments that usually require administration of between 100 mg and 1000 mg per dose. Low solubility in water means that several milliliters of antibody solution must be administered for administration of a single dose. Even assuming solubility as high as 50 mg/mL for the antibody, a 100 mg dose would require administration of 2 mL of solution, while a 1000 mg dose would require administration of 20 mL of solution. These volumes are too large for administration applications such as subcutaneous (SC), intramuscular (IM), intratumoral (IT) and intraarticular (IA) injections, which are generally limited to a 1 mL volume. It has, therefore, been necessary to administer these therapeutic agents as IV infusions. Such IV infusions are time consuming and inconvenient for medical staff and patients.
An additional limitation imposed by the relatively low solubility of antibody proteins is related to their production. After large-scale fermentation it is often desirable to hold material at an intermediate stage in order to combine several batches to create a large lot of product. The volume of the intermediate material must be sufficiently small to be conveniently stored at the manufacturing facility. Diafiltration of dilute solutions can lead to precipitation and membrane fouling. Large-scale freeze-drying requires significant investments in space, capital equipment and operating costs.
Attempts have been made to prepare highly concentrated antibody solutions by careful control of pH, ionic strength and buffer type, but many antibodies and other proteins cannot be dissolved at high concentrations even under the best of conditions. Also, even when it is possible to dissolve the antibody to a high concentration, it is still very difficult to maintain adequate protein stability in such high concentration solutions during long-term storage. In particular, the risk of formation of highly undesirable non-native aggregates increases as the concentration of the protein in the solution increases. Furthermore, the high viscosity exhibited by some high-concentration antibody solutions often complicates, and in some cases precludes, practical processing of the materials during manufacturing operations.
For reasons of product stability, therapeutic antibodies are currently supplied to clinical practices in lyophilized form. Freeze-dried vials are stored under refrigerated conditions and must be reconstituted prior to use. The reconstitution procedure is time consuming because lyophilized cake does not quickly reconstitute. Also, the reconstitution can result in degradation of the therapeutic protein through foaming and denaturation. The reconstitution process can therefore, lead to variability in both the administration dose and relative activity/immunogenicity of the therapeutic agent.
There is a significant need for improved high-concentration protein formulations, and there is especially a need for antibody formulations suitable for administration by applications such as SC, IM, IT and IA injection. There is also a significant need for improved techniques for processing and storing intermediate products during manufacture of antibody and other protein products. There is a further need for techniques for long-term storage of antibodies and other proteins that reduce or eliminate problems with reconstitution of lyophilized products.